1. The Field of Invention
The present invention relates to subcutaneously implanted cannulas used to access the body""s circulation. More particularly, this invention provides a cannula and method for establishing intermittent vascular access using an implanted cannula in the general shape of a xe2x80x9cTxe2x80x9d.
The advent of hemodialysis for the treatment of end-stage renal disease has prompted the development of many vascular access devices for the purpose of acquiring and returning large quantities of blood for passage through an extracorporeal circuit during hemodialysis procedure. Available devices have generally relied on the use of either indwelling venous catheters or flow through shunt devices which create an artificial fistula between an artery and vein.
Venous catheters are limited by relatively poor draw flows and by their tendency to be irritative resulting in vessel stenosis, thrombosis, and occasionally vessel perforation. They frequently fail because of infection, weakness in the vessel wall, poor catheter position, and/or thrombus formation in the catheter lumen. Shunt devices which create a fistulous blood flow between an artery and a vein have been the mainstay of modern vascular access for dialysis but are similarly problematic. Installation of these xe2x80x9cshuntsxe2x80x9d is an extensive surgical procedure resulting in significant tissue trauma and pain. Once in place, the shunts result in additional cardiac output needs with as much as one-fifth of the cardiac output (approximately 1000 ml per minute) required for adequate function. In addition, the transfer of the arterial pressure wave results in damage to the vein at the point of anastomosis with the shunt and can result in intimal hyperplasia and subsequent thrombosis and shunt occlusion. When such occlusion occurs, another vein segment must be used for shunt revision, and exhaustion of available sites is distressingly common and can be fatal. Repeated punctures of the wall of the shunt often result in eventual failure and require additional surgery to repair or replace the shunt. The expense in terms of both health care dollars and human misery is enormous.
Each of the available access technologies mentioned thus far are also complicated by the possibility of recirculation of blood already passed through the extra-corporeal circuit resulting in the loss of treatment efficiency. The harm done to patients by the xe2x80x9crecirculation syndromexe2x80x9d is insidious and at times undetected until great harm has been done.
Indwelling catheters which occupy only a portion of the vessel lumen are subject to movement within the vessel, which can cause irritation or even vessel perforation. Further, catheters which occupy only a portion of the vessel lumen, and which are inserted or threaded through the lumen for substantial distances tend to disrupt the normal flow of blood through the vascular structure, altering the hemodynamics of the blood flow in a manner which can damage the vessel, the components of the blood, and which can encourage thrombosis. Such catheters are generally unsuitable for long term implantation in arteries.
What is needed is a cannula that can be implanted within an artery and that will cause minimal disruption of blood flow through the lumen of the artery during use and nonuse of the cannula, which does not cause vessel stenosis, thrombosis, or vessel perforation, which is capable of handling large quantities of blood, and which will retain its usefulness for a long period of time after implantation.
2. Description of the Background Art
Vascular access employing indwelling catheters is described in a number of patents and publications including U.S. Pat. Nos. 3,888,249; 4,543,088; 4,634,422; 4,673,394; 4,685,905; 4,692,146; 4,695,273; 4,704,103; 4,705,501; 4,772,270; 4,846,806; 5,053,613; 5,057,084; 5,100,392; 5,167,638; 5,108,365; 5,226,879; 5,263,930; 5,281,199; 5,306,255; 5,318,545; 5,324,518; 5,336,194; 5,350,360; 5,360,407; 5,399,168; 5,417,656; 5,476;451; 5,503,630; 5,520,643; 5,527,277; and 5,527,278; and EP 228 532; and Wigness et al. (1982) paper entitled xe2x80x9cBiodirectional Implantable Vascular Access Modalityxe2x80x9d presented at the Meeting of the American Society for Artificial Internal Organs, Apr. 14-16, 1982, Chicago, Ill.
Catheters having distal valves are described in a number of patents including U.S. Pat. Nos. 274,447; 3,331,371; 3,888,249; 4,549,879; 4,657,536; 4,671,796; 4,701,166; 4,705,501; 4,759,752; 4,846,806; 4,973,319; 5,030,710; 5,112,301; 5,156,600; and 5,224,978.
Implantable dialysis connection parts are described in a number of patents including U.S. Pat. Nos. 4,692,146; 4,892,518; 5,041,098; 5,180,365; and 5,350,360.
The present invention provides improved implantable vascular cannulas which are particularly useful for providing long-term access to the arterial vasculature, including both native arteries and artificial arterial lumens (such as an arteriovenous (AV) shunt or an arterial graft. The cannulas of the present invention comprise a tubular body which is implantable within an arterial lumen and an access leg having one end attached to a side wall of the tubular body. Both the tubular body and the access leg have lumens therethrough, with the lumen of the tubular body being configured to receive the entire blood flow of the arterial lumen in which it is implanted. The access leg, which is attached to the tubular body in a generally T-shaped configuration, thus provides for access into the lumen of the tubular body for either withdrawing blood (e.g. for hemodialysis or other extra-corporeal treatment) or for introducing drugs or other media into the arterial blood flow.
The arterial access cannula may be implanted either subcutaneously or transcutaneously. By transcutaneous, it is meant that a portion of the access leg will pass outwardly through the patient""s skin to permit direct arterial access using external drug pumps, syringes, or other equipment. It will be appreciated, of course, that a hemostasis valve must be provided on the access leg to prevent uncontrolled blood loss. Usually, any transcutaneous use of the cannula of the present invention will be only for a short time.
More usually, the cannula of the present invention will be intended for subcutaneous use. In that case, an access port is connected to the open end of the access leg and is also subcutaneously implanted beneath the patient""s skin. The access port will be suitable for attachment to needles, tubes, catheters, and other devices which may be percutaneously introduced into the access port to provide a desired external connection. An example of an access port comprises a chamber having a penetrable membrane on one side thereof. Temporary access to the chamber is formed by penetrating the needle, tube, or catheter through the penetrable membrane.
In all cases, the T-configured arterial cannula of the present invention is an improvement over prior indwelling catheters in a number of respects. The tubular body is firmly anchored within the artery and not subject to being moved or dislodged by blood flow. Thus, trauma to the arterial wall from movement of the cannula is significantly lessened. Moreover, by assuring that the lumen of the tubular body has a cross-sectional shape and dimensions which closely match those of the arterial lumen, smooth blood flow through the cannula can be enhanced while the risk of thrombus formation is substantially reduced.
In a preferred construction, the arterial cannula will include an isolation valve, at or near the junction between the access leg and the tubular body. The isolation valve can be any type of valve that closes or inhibits flow between the tubular body lumen and the access leg lumen in the absence of a pressure drop therebetween. Thus, when blood is not being withdrawn and/or when drugs or other media are not being introduced, the isolation valve will close and isolate the lumen of the access leg from arterial blood flow. Such isolation is a significant advantage since it reduces the risk of thrombus formation within the access leg and thrombus release into the arterial lumen. Often, it will be desirable to flush the lumen of the access leg with an anti-coagulant fluid after each use. The removal of static blood and the placement of the anti-coagulant fluid further decreases the risk of thrombus formation and release. The isolation valve may be in a variety of forms, including slit valves, flap valves, ball valves, and may further be configured to provide for one-way or bi-direction flow. For example, in the case of arterial cannulas used for withdrawing blood, it will often be advantageous to have a one-way isolation valve which permits blood flow from the tubular body into the access leg, but inhibits reverse flow of any materials from the access leg into the lumen. In the case of drug and other infusions into the artery, it may be desirable to provide a one-way isolation valve which permits such introduction, but prevents reflux of blood into the access leg. A particularly preferred valve is a slit valve formed into the wall of the tubular body, as illustrated in detail hereinafter. When such a slit valve is closed, the inner profile of the tubular body lumen will be substantially smooth and free from discontinuities caused by the valve.
The arterial cannula may be formed from any one or a combination of a variety of biocompatible materials. By biocompatible, it is meant that the material(s) will be suitable for a long term implantation within patient vasculature and tissue and will be free from immunogenicity and inflammatory response. Usually, the cannula will be formed in whole or in part from an organic polymer, such as silicone rubber, polyethylenes, polyurethanes, polyvinylchloride, polytetrafluoroethylene (PTFE), polysulfone, or the like. Portions of the cannula may be reinforced, for example the access leg may include circumferential reinforcement to enhance its hoop strength without significantly diminishing flexibility. Such reinforcement may take the form of a helical wire or ribbon, axially spaced-apart hoops, or the like. Preferably, the reinforcement may be achieved by molding the access leg to incorporate circumferential corrugation, i.e. a plurality of axially spaced-apart circumferential ribs along all or a portion of its lengths. In all cases, it is desirable that the internal lumen of the access leg and the tubular body remain as smooth as possible to avoid disturbances to blood flow.
The tubular body of the arterial cannula will have dimensions compatible with implantation within a variety of arteries, including both native (natural) arteries and implanted synthetic arteries. The most common native arteries in which the cannulas may be implanted include the proximal ulnar, proximal radial, brachial artery, axillary artery, and subclavian artery. Implanted synthetic arteries include bypasses, shunts (e.g. AV shunts), arterial grafts, and the like. Both native arteries and implanted synthetic arteries have lumens, and reference to xe2x80x9carterial lumensxe2x80x9d herein is intended to refer to both such lumens.
Generally, the length of the tubular body will be in the range from 10 mm to 50 mm and the outer diameter will be in the range from 3 mm to 10 mm. The diameter of the lumen of the tubular body will generally be in the range from 1 mm to 8 mm. The access leg will usually have a length in the range from 25 mm to 700 mm and an outer diameter in the range from 3 mm to 10 mm. The lumen diameter of the access leg will generally be in the range from 2 mm to 8 mm.
In a preferred aspect of the present invention, at least a portion of the access leg of the arterial cannula will be sufficiently compliant so that substantially no forces are transmitted from the access leg back into the tubular body. For proper functioning of the arterial cannula, it is important that the tubular body remain properly aligned within the arterial lumen. This can be achieved by fabricating at least a portion of the access leg adjacent to the tubular body to have a low bending stiffness. The hoop strength of the access tube, in contrast, should remain relatively high, being at least sufficient to maintain patency of its lumen at internal pressures below xe2x88x92250 mmHg, preferably below xe2x88x92400 mmHg. Use of the helical reinforcement designs described above helps assure that the access leg can be sufficiently flexible while retaining sufficient strength.
In a first specific aspect of the present invention, a system for performing extracorporeal blood treatment comprises an arterial cannula as described above in combination with a venous cannula which is implantable within a venous lumen. The venous cannula will also comprise an access leg, but will usually be in the form of a conventional in-dwelling catheter or a distal portion of the cannula as within the venous lumen in a generally free or unrestricted manner. The use of conventional in-dwelling cannula in the venous vasculature is not problematic. Usually, both the arterial cannula and the venous cannula of the systems of the present invention will further include access ports intended to be connected to catheters for completing an extracorporeal circuit. Such access ports may be of generally conventional construction and may be connected to extracorporeal treatment circuits in a general conventional manner.
In another aspect, the present invention comprises a method for implanting an arterial access cannula within the lumen of an artery. The method comprises surgically exposing the artery and making an incision in its wall. The tubular body of the access channel is introduced through the incision and into the lumen of the artery. The lumen of the tubular body will be evenly circumferentially aligned with the arterial lumen, and the incision then closed. In some instances, the tubular body will have flared portions at either end, and the flared portions can optionally be tied within the artery to further anchor the cannula therein. The method may further comprise an initial step of determining a cross-sectional dimension of the artery and selecting a tubular body having a cross-section dimension substantially equal to that of the arterial lumen. The method may still further comprise subcutaneously introducing an arterial port, where the arterial port is connected or connectable to the access leg of the arterial access cannula. The arterial port may be introduced through the same incision as the arterial cannula. Alternatively, the arterial port may be introduced through a second incision formed remotely from the first incision, and the port thereafter connected to the access leg by forming a subcutaneous path between the two.
The method may still further comprise introducing a venous cannula by surgically exposing a vein, and introducing the venous cannula therethrough. The venous port may then be introduced, either through the same or a different surgical incision, in order to form a desired subcutaneous access assembly. By having introduced both an arterial cannula and a venous cannula, the patient is ready for access to hemodialysis or a variety of other extracorporeal treatment modalities.
In still further aspects of the present invention, methods are provided for performing extracorporeal blood treatment by percutaneously attaching a first catheter to an access leg of a subcutaneously implanted arterial cannula having a tubular body disposed within an arterial lumen. A second catheter is then percutaneously attached to a subcutaneously implanted venous access catheter, and blood may be circulated from the first catheter through an extracorporeal circuit to the second catheter. The first and/or second catheters are typically percutaneously penetrated to connect to the access leg, e.g. by penetrating a needle or needle-introduced catheter through a membrane of a conventional access port. The extracorporeal circuit may be hemodialysis, and the method may further comprise stopping blood circulation and filling at least the access leg of the arterial cannula with an anti-coagulant fluid.
In still a further aspect of the present invention, a method for administering a fluid medium into an artery comprises percutaneously attaching a needle or needle-introduced catheter to an access leg of a subcutaneously implanted arterial cannula having a tubular body implanted within the arterial lumen. The fluid medium is then infused through the needle or catheter into the access leg and from there into the lumen of the tubular body. The fluid medium will usually be a medication, but could also be a diagnostic or other conventional agent introduced to arterial blood flow.